1. Field of the Invention
This invention relates to flexible polyurethane foams made from aliphatic isocynanates and polyether polyols.
2. Description of the Prior Art
Flexible polyurethane foams are well-known materials having a variety of uses. A large body of information relating to the preparation of flexible polyurethane foams has been published in recent years. For example, Windemuth in U.S. Pat. No. 2,948,691 issued on Aug. 9, 1960 teaches that flexible polyurethane foams can be made from mixtures comprising aliphatic or aromatic isocyanates and polyols. Britain in U.S. Pat. No. 3,397,158 issued Aug. 13, 1968 and Hostettler in U.S. Pat. No. 3,398,106 issued Aug. 20, 1968 both describe an improvement in flexible polyurethane foam making processes through the use of stannous octoate catalyst.
Although there is some mention of aliphatic isocyanates, most of the information in the prior art relates to the use of aromatic diisocyanates, particularly tolylene diisocyanates, in making flexible polyurethanes. While flexible polyurethane foams having excellent physical properties can be prepared from aromatic isocyanates, they generally discolor on exposure to light. This discoloration is particularly undesirable in applications where aesthetic qualities of the foams are important. Wilson, in Australian patent application 416,687 published Nov. 30, 1967 describes a process for making flexible polyurethane foams having increased color stability. He suggests reacting polyester or polyether polyols having a molecular weight greater than 1,000 and hydroxyl numbers between 37 and 112 with aliphatic diisocyanates in the presence of polyfunctional hydroxyl compounds having at least three hydroxyl groups. Water, a metal catalyst, and, optionally, a basic amine catalyst are also required in the reaction mixture. While the process taught by Wilson represents an improvement over the prior art, the flexible polyurethane foams produced thereby still suffer from excessive surface tackiness, difficulties in manufacture because of long reaction times, and, in some embodiments, friability. These problems can be overcome through the use of the invention herein described.